1. Field of the Invention
The present invention relates to an ink jet recording method and an ink jet recorder, and specifically an ink jet recording method and an ink jet recorder which can control a number of ink droplets for forming a dot, and a storage medium for storing a program for driving the recorder.
2. Description of the Related Art
A known conventional ink ejector of the ink jet type has ink channels and nozzles each communicating with one of the channels. The volume of each ink channel can be changed by the deformation of a piezoelectric ceramic or the like. When the channel volume decreases, ink in the ink channel is ejected as droplets through the associated nozzle. When the channel volume increases, the ink channel is supplied with ink from an ink supply.
Such a conventional ink ejector 600 is shown in section in FIG. 6 of the accompanying drawings. The ink ejector 600 includes an actuator substrate 601 and a cover plate 602. The actuator substrate 601 has ink channels 613 and spaces 615 all in the form of grooves, which extend perpendicularly to a record medium set on the recorder including the ejector 600. The ink channels 613 and spaces 615 are arrayed alternately, with side walls 617 interposed between them, which are made of piezoelectric material. Each side wall 617 consists of a lower wall 611 and an upper wall 609, which are polarized in opposite directions P1 and P2, respectively. Each ink channel 613 has a nozzle 618 formed at one end. The other ends of the ink channels 613 are connected to a manifold (not shown), through which ink can be supplied. Those ends of the spaces 615 which are adjacent to the manifold are closed so that no ink can enter the spaces.
Both sides of each side wall 617 are fitted with a pair of electrodes 619 and 621 in the form of metallized layers. Specifically, the electrodes 619 and 621 are a channel electrode 619 and a space electrode 621, which are positioned in the adjacent ink channel 613 and space 615, respectively. All the channel electrodes 619 are grounded. The space electrodes 621 are connected to a controller 625 (FIG. 8), which outputs actuator drive signals. The space electrodes 621 on both sides of each ink channel 613 are connected together. The space electrodes 621 in each space 615 are insulated from each other.
When voltage is applied to the space electrodes 621 on both sides of any of the ink channels 613, the associated side walls 617 deform piezoelectrically in such directions that the channel or channels 613 enlarge in volume. As shown in FIG. 7 of the drawings, for example, in order to drive the side walls 617c and 617d for the ink channel 613b, a voltage of E volts is applied to the associated space electrodes 621c and 621d. The voltage application generates electric fields in opposite directions E in the side walls 617c and 617d. The electric fields deform the side walls 617c and 617d piezoelectrically in such directions that the ink channel 613b enlarges in volume, reducing the pressure in this channel 613b. This condition is maintained for the one-way propagation time T of a pressure wave in each ink channel 613. This supplies ink from the manifold to the ink channel 613b during the propagation time T.
The one-way propagation time T is the time that it takes for a pressure wave in each ink channel 613 to be propagated longitudinally of the channel 613. This propagation time T is L/a (T=L/a) where L is the length of the ink channel 613 and a is the sound velocity in the ink in the channel 613.
According to the theory of pressure wave propagation, exactly when the time T passes after the voltage is applied to the space electrodes 621c and 621d, the pressure in the ink channel 613b reverses into a positive pressure. When the pressure becomes positive, the voltage is returned to 0 volt. This allows the deformed side walls 617c and 617d to return to their original condition (FIG. 6) so as to apply a positive pressure to the ink in the ink channel 613b. This pressure is added to the pressure which has reversed to be positive. As a result, a relatively high pressure develops in that portion of the inkchannel 613b which is near to the nozzle 618b, ejecting an ink droplet through the nozzle.
If the period after the voltage is applied and until it is returned to 0 volt differs from the one-way propagation time T, the energy efficiency for the droplet ejection lowers. If this period is roughly an even number of times the propagation time T, no ink is ejected. Therefore, in general, in order to raise the energy efficiency, for example, to drive the side walls 617 at a voltage as low as possible, it is preferable that the period be roughly equal to the propagation time T or at least roughly an odd number of times the time T.
After an ink droplet is ejected from one of the ink channels 613 in accordance with a print instruction, vibration remains on the meniscus of ink in the associated nozzle 618. At some drive frequencies, the vibration affects the ejection of an ink droplet in accordance with the next print instruction. For example, the vibration may cause the ink droplet to be ejected in a wrong direction, or a needless ink droplet to be ejected.
FIG. 5 of the drawings shows printing with ink droplets ejected from one of the ink channels 613 in accordance with different patterns of print instructions at a higher drive frequency for printing at a higher speed. In accordance with the consecutive or serial print instructions, ink droplets can be ejected stably. In accordance with the print instruction for every other drive cycle (dot), that is a pair of print instruction and non-print instruction is repeated however, the influence of the ink meniscus in the associated nozzle 618 is amplified. This is liable to make ink droplets ejected in wrong directions and/or needless ink droplets ejected.
It is an object of the present invention to provide an ink jet recording method for good recording quality, which makes it possible to stably eject ink by changing the number of ejected ink droplets for a dot if the print instruction for the dot immediately follows and/or immediately precedes non-print instruction. It is another object to provide an ink jet recorder and a storage medium for use with such a recording method.
In accordance with a first aspect of the present invention, an ink jet recording method is provided for recording a dot pattern on a record medium by means of a recorder including an actuator, which has an ink channel filled with ink and a nozzle communicating with the ink channel. The ink channel can change in volume to eject ink from it through the nozzle. The recording method includes the steps of:
judging whether one print instruction for forming a dot immediately follows another or not and whether the one print instruction immediately precedes another or not; and
causing the actuator to eject a predetermined number of ink droplets for forming the dot depending on the result of the judgment.
The recording method makes it possible to stably eject ink, regardless of whether one print instruction for forming a dot immediately follows another or not, and regardless of whether the one print instruction immediately precedes another or not.
If the one print instruction for forming the dot immediately follows another and immediately precedes another, the predetermined number of ink droplets for forming the dot may be N which is two or more (Nxe2x89xa62). The number N may be three or four. If the one print instruction immediately follows and immediately precedes no others, the number of ink droplets may be M which is smaller than N (M less than N). As vibration remained on the meniscus of ink in the nozzle increases, a number of ejections increases because the vibration corresponds to vibration in pressure which is accumulated thereto each time an ink droplet is ejected from the nozzle. Accordingly, if the number M of ink droplets is smaller than N (M less than N), the vibration can be reduced.
If the one print instruction immediately follows or immediately precedes no other when the temperature of the ink or the ambient temperature around the ink is lower than a predetermined temperature, the predetermined number of ink droplets may be N (Nxe2x89xa62). If the one print instruction immediately follows or immediately precedes no other when the ink temperature or the ambient temperature is equal to or higher than the predetermined temperature, the number of ink droplets may be M (M less than N).
By reducing the number of ink droplets, it is possible to restrain the influence of the residual vibration of the ink meniscus in the nozzle to stably eject the droplets. Even if the viscosity of the ink changes with temperature, it is possible to keep the ejection stable.
The number M may be N minus one (M=Nxe2x88x921). In this case, if the one print instruction immediately follows and/or immediately precedes no other, one or more ink droplets which are only one fewer than the number N are ejected for the dot. This makes it possible to restrain the influence of the residual vibration of the ink meniscus in the nozzle, and to stably eject the ink droplets similar in total volume to those for serial printing.
In accordance with a second aspect of the present invention, an ink jet recorder is provided. The recorder includes an actuator having an ink channel which can be filled with ink and a nozzle communicating with the ink channel. The ink channel can change in volume to eject ink from it through the nozzle to record a dot pattern on a record medium. The recorder also includes a judgment device for judging whether one print instruction for forming a dot immediately follows another or not and whether the one print instruction immediately precedes another or not. The judgment device may be a circuit for driving the actuator. The recorder also includes a driver for driving the actuator to eject from the actuator for forming the dot a predetermined number of ink droplets depending on the result of the judgment.
The recorder may further include a storage device storing in it the relationship between the predetermined number of ejected ink droplets or ejection waveform and the presence/absence of print instructions immediately preceding and immediately following the one print instruction.
If the judgment device judges that the one print instruction immediately follows another and immediately precedes another, the driver may drive the actuator to eject a number N of ink droplets which are at least two (Nxe2x89xa62). The number N may be three or four. If the judgment device judges that the one print instruction immediately follows and immediately precedes no others, the driver may drive the actuator to eject a number M of ink droplets fewer than the number N (M less than N). The number M may be N minus one (M=Nxe2x88x921).
By reducing the number of ink droplets, it is possible to restrain the influence of the residual vibration of the ink meniscus in the nozzle to stably eject the droplets.
The recorder may further include a temperature sensor for measuring the temperature of the ink or the ambient temperature around the ink. If the one print instruction immediately follows or immediately precedes no other when the measured temperature is lower than a predetermined temperature, the actuator may eject ink droplets which are N (Nxe2x89xa62) in number. If the one print instruction immediately follows or immediately precedes no other when the measured temperature is equal to or higher than the predetermined temperature, the actuator may eject ink droplets which are M (M less than N) in number. This makes it possible to keep the ejection stable even if the viscosity of the ink changes with temperature.
In accordance with a third aspect of the present invention, a storage medium is provided which stores in it a program for use with an ink jet recorder including an actuator. The actuator has an ink channel which can be filled with ink and a nozzle communicating with the ink channel. The program drives the actuator so that the ink channel changes in volume to eject ink from it through the nozzle to record a dot pattern on a record medium. The program includes the steps of:
judging whether one print instruction for forming a dot immediately follows another or not and whether the one print instruction immediately precedes another or not; and
controlling the actuator to eject from the actuator a predetermined number of ink droplets for forming the dot depending on the result of the judgment.
The program may further include the steps of:
selecting, as the predetermined number of ink droplets for forming the dot, a number N if the one print instruction immediately follows another and immediately precedes another, the number N being at least two (Nxe2x89xa62); and
selecting, as the predetermined number of ink droplets for forming the dot, a number M if the one print instruction immediately follows and immediately precedes no others, the number M being smaller than the number N (M less than N).
The number N may be three or four. The number M may be N minus one (M=Nxe2x88x921).
The program may further include the step of selecting, as the number of ink droplets for forming the dot, the number N (Nxe2x89xa62) if the one print instruction immediately follows or immediately precedes no other.
The program may include the step of selecting, as the number of ink droplets for forming the dot, the number M (M less than N) depending on the temperature of the ink or the ambient temperature around the ink if the one print instruction immediately follows or immediately precedes no other.
The program may be driver software for controlling a driver circuit for the actuator.
The storage medium may have data stored in it on different waveforms for the actuator.